Residents of San Ysidro called a second protest in three weeks over raw sewage flowing from Tijuana into the Tijuana River Valley. The rally is set for Wednesday, April 22, at 1 p.m. near the El Super market at 350 W. San Ysidro Boulevard. Organizers say hydrogen sulfide readings in the area have hit 4,500 parts per billion, roughly 150 times California’s alert threshold of 30 ppb, and they want the smell and the health risk gone now, not in 2028.
Hydrogen Sulfide at 150 Times California’s Alert Level
Hydrogen sulfide is the colorless gas behind the rotten-egg smell that hangs over neighborhoods near the Tijuana River channel. California sets its public alert threshold at 30 ppb. In the San Ysidro corridor, monitors have logged sustained readings of 750 ppb over multiple hours. Peak spikes have reached 4,500 ppb.
At concentrations above 100 ppb, the gas can cause eye irritation and respiratory distress. Prolonged exposure above 500 ppb can trigger headaches, nausea, and more serious lung inflammation. Residents near Coral Gate Park and along Sunset and Smythe avenues say they experience these symptoms daily.
The source is organic matter decomposing in untreated wastewater that flows north through the river channel. Industrial waste, plastics, and chemical runoff mix with raw sewage on the Tijuana side, then cross the border and contaminate both the air and the ocean at Imperial Beach. The problem is not new. Cross-border sewage flows have plagued the Tijuana River Valley for decades, but residents say the current episode, which began in November 2025, is among the worst.
SEPROA Blames U.S. Floodgate Repairs for November 2025 Overflow
After the first protest on April 7 outside Smythe Elementary School, Baja California’s water agency responded publicly. SEPROA (the state secretariat for water management, sanitation, and protection) secretary Víctor Daniel Amador Barragán said the overflows stem from U.S. repairs to a floodgate known as JB1. That gate sits on the international boundary and controls storm and wastewater flows between the two countries.
Amador Barragán said U.S. work on the gate has caused sewage to back up and spill since November 2025. “It is not work that we are doing,” he told reporters. He added that Baja California has carried out its own sanitation projects and continues to meet commitments under a binational agreement.
Residents are unconvinced. They point out that cross-border sewage predates any floodgate repair. The Tijuana River has carried untreated Mexican wastewater into U.S. territory for years because Tijuana’s sewer system lacks the capacity to handle the city’s roughly two million residents. CESPT, Tijuana’s municipal water and sewer utility, operates aging infrastructure that routinely overflows during rainy seasons. Dry-weather spills also occur when pump stations fail or pipes break.
On the U.S. side, the International Boundary and Water Commission (IBWC) operates the South Bay International Wastewater Treatment Plant in San Ysidro. That facility was designed in the 1990s to treat 25 million gallons per day of diverted Tijuana sewage. Congress approved roughly $300 million in supplemental funding through the U.S.-Mexico-Canada Agreement (USMCA) implementation to expand capacity and build new treatment infrastructure. But construction timelines stretch to 2028 and beyond.
Binational Fix Targets 2028, but Residents Smell the Problem Today
The 2028 target date comes from a binational framework that pairs IBWC upgrades on the U.S. side with Mexican commitments to repair collectors, pump stations, and treatment capacity in Tijuana. Mexico’s federal water commission, CONAGUA, and SEPROA share responsibility for the Mexican side.
Yet funding and execution have lagged on both sides of the border. On the Mexican side, federal austerity budgets under the current administration have slowed infrastructure spending. On the U.S. side, the expanded treatment plant and a planned new “Tijuana River Diversion” system remain in planning and early construction phases. Even optimistic timelines place full operational capacity several years out.
For anyone living or working in the San Ysidro corridor, the gap between 2025 and 2028 means continued exposure. The neighborhoods most affected, including areas around Coral Gate Park, Beyer Boulevard, and the Smythe Avenue corridor, sit within a mile of the river channel. On still, warm days, hydrogen sulfide concentrations climb. Residents report keeping windows closed year-round and pulling children indoors during afternoon hours when readings spike.
If you commute through the San Ysidro port of entry, you pass through this zone daily. The El Super market where Wednesday’s protest will gather sits just blocks from the border crossing. Pedestrians and drivers waiting in line are exposed to the same air.
Organizers say they will continue staging periodic demonstrations until conditions change. Wednesday’s protest is their second since April 7 and likely not their last. The binational agreement’s next milestone review is scheduled for late 2026, as reported by Punto Norte.